The present invention relates to antitheft systems for protecting merchandise on display in stores from unlawful acts such as shoplifting, and more particularly to an antitheft system which comprises a signal transmitter incorporated, for example, in an antitheft gate for producing an alarm activating signal, and a self-sounding alarm unit attached to a commodity or like article to be protected from theft and adapted to generate sound in response to the alarm activating signal received from the signal transmitter.
FIG. 9 shows an antitheft system conventionally used in stores wherein commodities such as compact disk cassettes and magnetic tape cassettes are on display for sale, to protect these articles from shoplifting or like illegal acts.
The antitheft system comprises an antitheft gate 2 installed in the vicinity of an exit 5 of the store, and an alarm unit 4 attached to a commodity 6. The antitheft gate 2 has a circuit board 21 and a transmitting antenna (not shown) which are incorporated therein. The circuit board 21 is provided with a transmitting circuit for producing an alarm activating signal for the alarm unit 4.
With reference to FIG. 10, the alarm unit 4 comprises a buzzer 41, circuit board 42, battery (not shown), etc. which are housed in a casing 40. The casing 40 has a surface provided with sound emitting holes 43 and an alarm actuating switch piece 44 projecting therefrom. The buzzer 41 has its operation controlled by the circuit board 42 and is adapted to produce an alarm when the unit 4 is removed from the commodity 6 or when the unit 4 passes by the antitheft gate 2.
The commodity 6 is placed on display in the store, with the alarm unit 4 attached thereto. When selling the commodity to the customer, the clerk holds the buzzer 41 out of operation by sending a specified signal to the circuit board 42 of the alarm unit 4 from a nullifying device (not shown), then removes the unit 4 from the commodity 6 and hands the commodity 6 to the customer in exchange for money.
If the customer wrongfully removes the alarm unit 4 from the commodity 6, the switch piece 44 is turned off to actuate the buzzer 41. Further if the customer acts to unlawfully bring the commodity 6 out of the store along with the alarm unit 4, the circuit board 42 of the alarm unit 4 receives an alarm activating signal from the transmitting antenna of the antitheft gate 2 to turn on the buzzer 41.
FIG. 11 shows the electrical construction of the alarm unit 4.
The alarm unit 4 has a receiving antenna 46 comprising a coil and a capacitor and connected to a control circuit 48 via a signal amplification circuit 47. The aforementioned battery (primary battery) 45 is connected to the signal amplification circuit 47 and the control circuit 48. These circuits 47, 48 are energized by the primary battery 45 to operate as specified. The control circuit 48 is provided with the alarm actuating switch piece 44 and has the buzzer 41 connected thereto.
The receiving antenna 46 receives a signal, which is fed to the amplification circuit 47 for amplification and then fed to the control circuit 48. The control circuit 48 judges whether the signal fed from the amplification circuit 47 is an alarm activating signal from the antitheft gate 2, and gives a drive command to the buzzer 41 if the signal is the activating signal. The control circuit 48 further detects opening of the alarm actuating switch piece 44 when it is turned off, giving a drive command to the buzzer 41. Thus, the buzzer 41 goes on in response to the drive command given by the control circuit 48.
With the alarm unit 4 of the type described, the primary battery 45 incorporated therein is replaced when the life of the battery 45 terminated. The alarm unit 4 is usually attached to each commodity in the store, and many alarm units 4 are in use. It is therefore likely that the primary batteries of many alarm units 4 need to be replaced at the same time. The replacement of batteries of many alarm units 4 is very cumbersome and costly. It is accordingly required to suppress the power consumption of the alarm unit 4 to the greatest possible extent.
However, the conventional alarm unit 4 is so adapted that whenever electromagnetic waves from one source or another are received by the receiving antenna 46, the control circuit 48 judges whether the waves are an alarm activating signal from the antitheft gate 2. When a commodity having the alarm unit 4 attached thereto is on display as positioned, for example, in the vicinity of an inverter fluorescent lamp, the electromagnetic waves emitted by the lamp at all times are received by the antenna 46, permitting the control circuit 48 to continuously perform the signal judging operation, hence the problem of wasting electric power to shorten the battery life. The life of the primary battery 45 is about 3 to about 5 years when the alarm unit 4 is not exposed to the electromagnetic waves from the inverter fluorescent lamp, whereas the life becomes shortened to 1 to 2 weeks if the unit 4 is held exposed to noise signals.
An object of the present invention is to provide an antitheft system comprising an alarm unit which is adapted to suppress the shortening of battery life due to useless power consumption.
The present invention provides an antitheft system comprising an alarm unit attachable to an article to be protected from theft, and a signal transmitter for transmitting an alarm activating signal to the alarm unit, the alarm unit comprising:
receiving means for receiving signals from outside,
alarm means for producing an alarm in response to an alarming command,
nullifying means operable in response to a nullifying command to nullify the signal received by the receiving means for a predetermined period of time subsequent to the reception of the nullifying command, and
control means operable upon reception of the received signal from the receiving means to judge whether the received signal is the alarm activating signal and give the alarming command to the alarm means when the signal is the alarm activating signal or give the nullifying command to the nullifying means when the signal is not the alarm activating signal.
In the case where the antitheft system of the invention is installed in a store, the commodities to be protected against theft are placed on a display counter, with the alarm unit attached to each commodity, while the signal transmitter is disposed in an warning area in the vicinity of the exit of the store.
The receiving means of the alarm unit in this state is likely to receive external noise signals, such as electromagnetic waves being emitted by electric lamps. At this time, the control means judges whether the received signal is an alarm activating signal. Upon finding that the received signal is not the alarm activating signal, the control means gives a nullifying command to the nullifying means, which in turn nullifies the received signal for a predetermined period of time subsequent to the reception of the signal. This period of time is such that will cause no trouble to the operation of the alarm unit to be described below, e.g., 200 msec. Consequently, the control means is forced to cease the signal judging operation for the predetermined period of time despite the reception of signals by the receiving means. Accordingly, if the display counter is positioned in the vicinity of an inverter fluorescent lamp, the receiving means will receive the electromagnetic waves being emitted by the fluorescent lamp at all time, while the control means performs the signal judging operation intermittently.
If the customer passes through the warning area in the vicinity of the store exit in an attempt to wrongfully bring a commodity out of the store, the receiving means of the alarm unit attached to the commodity will receive an alarm activating signal from the signal transmitter, and the control means judges whether the received signal is the alarm activating signal during a period other than the predetermined period mentioned. Upon finding that the received signal is the activating signal, the control means gives an alarming command to the alarm means, which in turn produces an alarm, thus notifying the clerk of the unlawful act.
In the case where the display counter is disposed in the vicinity of an inverter fluorescent lamp, the control means intermittently performs the signal judging operation as described above, so that the alarm unit of the present invention is smaller in useless power consumption by the control means than the conventional alarm unit wherein the signal judging operation is performed continuously in such a case. This suppresses the shortening of the battery life.
Stated more specifically, the nullifying means of the alarm unit comprises a gate circuit interposed between the receiving means and the control means and operable in response to the nullifying command to prevent the signal received by the receiving means from passing through the gate circuit for a predetermined period of time subsequent to the reception of the nullifying command.
When the signal received by the receiving means is not the alarm activating signal and even if a signal is received by the receiving means during the subsequent predetermined period of time, the received signal is prevented by the nullifying means from passing through this means and is not input to the control means. The control means is therefore held out of the signal judging operation.
Further stated more specifically, the alarm unit comprises signal processing means capable of processing as specified the signal received by the receiving means and feeding the processed signal to the control means while being supplied with electric power, and power source means for supplying electric power to the signal processing means, and the nullifying means comprises a deenergizing circuit operable in response to the nullifying command to cease the supply of electric power from the power source means to the signal processing means for a predetermined period of time subsequent to the reception of the nullifying command.
When the signal received by the receiving means is not the alarm activating signal in the case of the alarm unit thus constructed, the supply of electric power from the power source means to the signal processing means is ceased for the subsequent predetermined period of time, rendering the signal processing means unable to perform the specified signal processing operation. Even if a signal is received by the receiving means during the predetermined period of time, it is therefore unlikely that the received signal will be input from the signal processing means to the control means, and the control means is held out of the signal judging operation.
When the display counter is positioned in the vicinity of an inverter fluorescent lamp as described above, electric power is intermittently supplied from the power source means to the signal processing means in the case of the construction described above, hence reduced power consumption by the signal processing means. This further diminishes useless power consumption.
Stated further specifically, the control means of the alarm unit judges whether the received signal is the alarm activating signal in response to a clock signal supplied from outside, and the alarm unit further comprises clock supply means for supplying the clock signal to the control means, and a clock halting control means for ceasing the clock signal supplying operation of the clock supply means for the predetermined period of time when the received signal is not found to be the alarm activating signal.
When the signal received by the receiving means is not the alarm activating signal in the case of the alarm unit thus constructed, the operation of the clock supply means for supplying the clock signal to the control means is ceased for the subsequent predetermined period of time. Since the control means is forced to cease the signal judging operation for the predetermined period of time as already described, the cessation of supply of the clock signal to the control means causes no trouble to the operation of the control means.
When the display counter is positioned in the vicinity of an inverter fluorescent lamp as described above, the clock supply means intermittently performs the clock signal supplying operation. This feature of the construction described reduces the power consumption by the clock supply means, consequently further diminishing useless power consumption.
As described above, the antitheft system according to the present invention diminishes the useless power consumption by the alarm unit to thereby suppress the shortening of battery life.